Related Links

Delta Air Lines has raised fares by $20 round-trip on tickets purchased within seven days of departure, a spokesman has confirmed.

It is the ninth attempt to raise fares this year. Only two have been successful so far, and they were led by Delta.

Typically, when Southwest Airlines and other low-cost carriers do not match the increases, they tend to be rolled back.

Rick Seaney, founder of FareCompare.com, which tracks fares, says the latest hike appears to be aimed at business travelers who are more inclined to buy last-minute fares. "Such last-minute purchases are largely the realm of the road warrior," he said in an email.

Airlines have been more reluctant to try to raise fares this year compared to years past. Last year, there were 15 attempts to raise fares, with seven succeeding. In 2011, there were 22 tries, with nine sticking.

As of Tuesday afternoon, spokesman for United and US Airways said they had not yet matched the fare increase. Southwest Airlines and JetBlue Airways did not respond to emails asking for comment.